Investigating Yeast


Last week, Class 4 were investigating yeast and set up an experiment to discover in which conditions yeast rises. The experiment required 4 zip up freezer bags which were then filled with different elements.

Each bag contained yeast and then:

Bag A - sugar and warm water

Bag B - sugar and cold water

Bag C- sugar, salt and warm water

Bag D- no sugar and warm water


We discussed fair testing and the variables that would need changing. We made a prediction as to the results and then observed to gather our results, 

It was Bag A which contained yeast, sugar and warm water where the yeast rose successfully. It did not rise in the other bags This is because yeast requires the sugar in order to feed and it also requires warm and moist conditions - this was provided by the warm water. Carbon dioxide was then released causing the bag to inflate and the yeast to rise. We found out that salt kills the yeast and that it does not rise in cold water.